The Research On IP Header Compression Algorithms In Wireless Internet Access

It is expected that the new telecommunication systems will be based on the convergence between mobile telephony and Internet providing a wide variety of services independently of user location. In this scenario is being developing the third generation (3G) mobile system: a true mobile service convergence of voice, data and image. Actually, the only way to make the 3G mobile system convenient, seems to be a network platform totally based on IP protocol, called "all-IP network", that includes wireless links, whose bandwidth is the most precious resource of the whole wireless system. However, the encapsulation process of the hierarchical transmission protocols wastes a substantial part of the wireless bandwidth for the transmission of control information (header) that do not have any specific function for the management of wireless channel itself.This problem becomes much worse for real time voice services, which will continue to be dominant in future mobile systems. For such services, speech data will most likely be carried by RTP. A packet will then have an IP header (20 octets), a UDP header (8 octets), and an RTP header (12 octets) for a total of 40 octets. With IPv6, the IP header is 40 octets for a total of 60 octets. However, the size of the payload depends on the speech coding and frame sizes being used and may be as low as 15-20 octets. It is obvious that 67-80% of wireless channel bandwidth is wasted for headers transmission and only the 20-33% of bandwidth is used for the transmission of real information for the final users.For wireless systems, the scarce wireless resources must be utilized efficiently in order to provide mass-market services at reasonable prices. The header overhead introduced by transmission protocols must be reduced by header compression. Through the significant reduction of the header size, for the same application we have a lower demand of bandwidth (lower cost) as well as greater efficiency and responsiveness.The error-proneness (the bit error rate as high as 10e-3, even 10e-2) and the large delays (the round trip time as high as 100-200ms) of wireless links make headercompression as defined in CRTP (Compressed RTP) perform less than well. RObust Header Compression (ROHC) scheme has been just proposed by the IETF working group, which aims at providing a compression scheme that has high compression efficiency and high robustness when used over wireless links.Based on the analysis on ROHC scheme, this paper mainly focuses the research on the following four topics:(1) The multipath fading on a wireless channel is considered to follow a Rayleigh distribution. The issue of modeling burst error process on a correlated Rayleigh fading channel has been addressed in many papers, where it was shown that, for a broad range of pa-rameters, the sequence of data block success and failure can be approximated by means of a simple finite state Markov models. The finite state Markov models accu-rately represent this type of burst error behavior of wireless channel by transitioning with a different probability between every state, each having a different error prob-ability and a different duration.However, all of existing header compression schemes do not take wireless chan-nel state into consideration when designed. When used in wireless links, they act in the invariable way when wireless channel enters into different states. In addition, they just adopt variations of encoding methods and repair mechanisms to minimize the number of lost packets when error happens over wireless links. These known header compression schemes can't work very well over wireless links because they lack of flexibility to handle different wireless channel states. If the current channel state can be predicted, the header compression scheme may take some different effective ac-tions and mechanisms according to the current channel state in advance of compress-ing headers, when wireless channel enters into different states. Obviously, this type of header compression scheme may suit much better to be used over wireless links.Based...